1. Field of the Invention
This invention relates to electrotherapeutric devices, and more particularly to apparatus for applying two separate frequencies of electrotherapeutic currents to the body of the patient each of said frequency currents being applied as a repeating series of pulses with a predetermined waveshape during a predetermined period.
2. Description of the Prior Art
From the earliest times of electrical knowledge, the response of organic tissue to the stimulus of electric current has been known. The first detailed scientific investigation of these effects was performed in Italy by Luigi Galvani, professor of anatomy at the University of Bologna. Due to the primitive state of development of electrical equipment in this era, his work was of necessity limited to application of steady-state DC and very low frequency (manually pulsed) AC. Galvani also observed and investigated the effects upon organic tissue of the induced energy resulting from the spark discharge of a nearby electrostatic generator, such discharges being largely oscillatory in nature and containing components of several frequencies.
Many studies were performed during the 19th century by many workers involving the application of electrical currents to the human body for medical purposes, with such studies devoted to the effects of various intensities, frequencies, directions of current flow, and electrode arrangement. Various apparatus for applying electrotherapeutic currents to the body of a patient have been developed. For example, U.S. Pat. No. 1,425,743 - Baruch which issued in 1922 covered an apparatus which produced an alternating electrostatic field of a plurality of different frequencies so that a hetrodyne effect was produced within the tissue of the patient. Similarly, French Pat. No. 859,618 published Dec. 23, 1940 describes an electrotherapeutic method which comprises the application to the body of two high frequency currents which intersect within the tissue of the patient so that upon intersection, a beat frequency equal to the difference between the two high frequencies resulted and was experienced by the patient. Similar heterodyne effect electrotherapeutic devices have been developed. For example, U.S. Pat. No. 2,622,601 - Nemec and U.S. Pat. No. 3,096,768 - Griffith disclose electrotherapeutic devices for producing and applying two separate signals of different frequencies to the body of the patient to produce heterodyne "beat" frequency sensation. Our own U.S. Pat. No. 3,794,022 discloses a dual oscillator, variable pulse duration electrotherapeutic device for producing series of square wave voltage pulses at two different frequencies, with the square wave pulses increasing in duration during repeating intervals, and the two frequencies intersecting within the body.
As is well known in the art, the stimulating effect of therapeutic electrical current is dependent on the form of the individual impulses and the frequency and intensity of the pulses. Furthermore, it is a well-known phenomenon of human physiology that a constant application of a sensoral stimuli to the nervous system has the effect of desensitizing the nerves over a period of time. Consequently, if the purpose of the electrotherapeutic device is to produce an anaesthesia of a particular portion of the body, a constant unvarying electrotherapeutic current should be applied to the area. However, where it is desired to limit the desensitization of the area to be treated, a constantly varying electrotherapeutic impulse should be applied to the area to be treated such as described in applicants' U.S. Pat. No. 3,794,022, issued Feb. 26, 1974.
Further, to provide maximum therapeutic reults, it is often desirable to apply various frequencies of electro-therapeutic current to the body of the patient. However, rather than utilizing the heterodyne effect between two frequencies to create a low frequency sensation to the patient, essentially the same sensation may be created by applying pulsed currents of a very low frequency.